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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4059
Hi all. Just started another project, testing/diagnosing memory cards.
So far, I've built a USB test jig which reads the current drawn by the reader. Tested with 3 cards. Results below. R = 18 ohms, to scale current to my meter's most sensitive range. With 256MB xD Quiescent = 0.787V Reading is between 0.804V and 0.847V Writing is between 1.051V and 1.074V
With 2GB xD Quiescent = 0.847V Reading is around 0.946mA Writing is between 1.270V and 1.294V
With 32MB (!) MMC Initial current = 0.781V Quiescent = 0.994V when just accessed Reading is between 1.153V and 1.174V Writing is between 1.417V and 1.449V
To get actual current, subtract the reader's own current draw i.e. 0.715V from these readings. Then divide by 18.0 to get the exact current used by the card(s). From this you can see that the larger cards draw more power than the smaller ones.
This would also be an effective way to measure the number of layers in a given card, when its capacity is known. A 4GB uSD would have 2 chips layered whereas a 32GB would have 17 or 9 depending on its technology. As all the chip buffers need to be powered this would also let you locate a bad card or a FakeFlash.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Conundrum wrote ...
...To get actual current, subtract the reader's own current draw i.e. 0.715V from these readings. Then divide by 18.0 to get the exact current used by the card(s)...
can you explain this further? im not folowing your logic here.
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Hacking memory cards
I don't see how the reader can work properly with 1.4V dropped off its supply rail.